The present invention relates to a method for correcting imbalance of vehicle tires, preferably tubeless tires with a radial carcass for passenger cars with wheel rims that have a 5.degree. seat surface whereby each tire is first mounted onto a master wheel rim that, in addition to having been manufactured with great precision, corresponds substantially to the commercial wheel rims of the corresponding tire, which tire is subsequently inflated to a pressure within a range of -0.3 bar to +0.2 bar of the preset maximum operating pressure. Subsequently, the wheel comprised of the master wheel rim and the tire to be corrected is pressed against a measuring device, for example, a roller shaped force measuring device, and at least one radial parameter is measured, preferably electronically, as a function of the rotational angle of the wheel covering the complete range of 0.degree. to 360.degree.. The values of the radial parameter are recorded and, subsequently the minimum and the maximum values are determined. Then the difference between the two extreme values, i.e., the maximum force, respectively, maximum radius deviation, is determined and this difference is compared with the allowed maximum threshold value, whereafter the tires, the maximum deviation of which surpasses a preset tolerance value, are subjected to a correction within the bead area.
Such a prior art method is disclosed in German Offenlegungsschrift 27 15 111. The disclosed method is designed to reduce imbalances, especially dynamic imbalances of the tire. For this purpose, on the axially inner side of the tire bead additional rubber is supplied for subsequent trimming operations (see FIGS. 2 and 3 of the disclosure) or is removed at opposite locations.
Since it is not necessary to balance the tire and the wheel rim independently, and since it is essentially sufficient to balance both together with the other components that make up the finished wheel, for example, the valve and optionally the brake disks, respectively, the brake drums, and since furthermore a fixation of the balance weights at the wheel rim can be realized very easily, especially without having to mount the tire again after imbalance measurement, the described prior art method has not been used in practice. Furthermore, the chassis vibrations that can be detected in the interior of the vehicle on a planar road surface are not only the result of non-uniform mass distribution that can be compensated by balancing, but furthermore also depend on stiffness and radius fluctuations.
In the following it is presupposed that according to conventional methods the mass distribution of a wheel can be made sufficiently uniform by correct placement of balance weights. Thus, the object remains to reduce the still present force fluctuations, especially of the radial force, to a tolerable magnitude. The value of tolerable magnitude is essentially determined by the customer and depends essentially on the comfort level expected within a vehicle class, the ratio between the sprung and unsprung masses, the maximum allowable, respectively, maximum possible velocity, and also the willingness to pay a higher price for an optimized balancing of the tires. For a conventional wheel contact force of approximately 3,150 Newton on the higher load axle of contemporary mid-size vehicles, the initial manufacturer's tire package for a new car conventionally allows for a maximum fluctuation of the radial force (=maximum-minimum) over the circumference of approximately 100 Newton which corresponds to +/-1.6%.
Since not all tires after vulcanization fulfill such balance requirements, it is known to correct the tires, which do not correspond to the aforementioned tolerance range, after vulcanization. In Germany, the term of the art for such a process is harmonizing. The conventional harmonizing process is comprised of grinding the tread surface. This method thus accepts the fact that the depth of the tire tread is locally reduced. However, this measure can only be applied within very small limits, conventionally of up to 0.5 mm.
European Patent 0 405 297 teaches that for tires that are mounted onto 5.degree. wheel rims a different harmonizing method can be employed. So-called 5.degree. wheel rims are conventional on all passenger cars and lightweight commercial vehicles such as Ford Transit, VW bus, Renault Traffic etc. According to the disclosed method, between the rim flanges which extend substantially vertically to the axis of the tire and the corresponding bead surface a washer-type disk is to be placed the thickness (axial dimension) of which is proportional to the imbalance to be compensated: at locations where the measured radial force is greater than the average radial force over the circumference, the washer-type disk is to be extra thick and at locations where the actual radial force is smaller than the average radial force the washer-type disk is especially thin. With such a compensation measure it is indeed possible to reduce the peak/peak values of the radial force function over the circumference. However, the tire bead in this arrangement is positioned on the wheel rim further axially inwardly, where the wheel rim diameter is smaller, and the contact pressure between the radial inner bead surfaces, especially of the sealing toe, and the wheel rim seat surface is reduced. This negatively effects the throw-off safety. Even at locations where the radial force without correction is within the tolerance range, the bead of the tire is axially inwardly displaced because the washer-type disk must have a minimum thickness for reasons of rigidity and stiffness. Furthermore, the radially inwardly displaced and thus axially inwardly pulled sidewall of the tire results in a reduction of the edge climbing capability of the wheel as known from wheel rims with narrowly spaced rim flanges. This will result in problems especially for vehicles that are mostly used in inner city traffic. Also, this increases the likelihood of damage to the wheel rim flanges when contacting the curb edges.
Furthermore, it is in general undesirable to increase the number of components to be joined because this increases the likelihood of incorrect mounting which could lead to enlarging the imbalance to be compensated.
The same patent disclosure also teaches for so-called 15.degree. wheel rims (conventionally employed for medium-size and heavy trucks) to use such washer-type disks that are to be adapted in their thickness over the circumference of the wheel rim to the radial force function and are to be positioned between wheel rim and tire bead. The suggested position is not between wheel rim flange and bead surface, but between the radially inner seat surface of the wheel rim that is slanted at an angle of 15.degree. and the matching bead surface. The thickness (radial dimension) should be selected proportional to the imbalance to be compensated whereby at locations where the local radial force is greater than the average radial force over the circumference, the washer-type disk should be especially thin and at locations where the actual radial force is smaller than the average radial force, the washer-type disk should be especially thick.
This method, which requires the use of smaller seat surface diameters of the wheel rim when using conventional tires or an increased bead diameter of the tires when using conventional wheel rims in order to provide sufficient radial constructive space for the washer-type disks designed to compensate for the radial forces, increases not only the parts needed to mount a wheel, but also increases the number of parts for each type of vehicle. This is in practice unacceptable.
It is therefore an object of the present invention to provide a correcting method for reducing at least the radial force fluctuations of pneumatic vehicle tires which does not require additional parts for the wheel and which also does not increase the multiplicity of parts. Furthermore, any negative effect on other tire properties should be avoided. Especially the edge climbing capability and protection of the flange of the wheel rim should remain unaffected.